Signal multiplexing is becoming increasingly widespread. Many new custom multiplexing structures are being developed. The communications market demands inexpensive, high-quality, flexible systems worldwide to meet growing customer demands. A summary of several of the digital multiplexing methods being used is provided for background purposes.
Time Division Multiplexing (TDM)
Time division multiplexing is a method of transmission where all individual users share the same available bandwidth divided into time segments or time slots (see FIG. 1).
Today there are many different types of multiplexors. Some maintain a standard structure and some are custom configured specifically for the user. Multiplexing structures have some basic characteristics in common such as synchronization, time slots and channel allocations, frame rates, and frame widths. Any or all of these characteristics may be altered to create a new multiplexing structure. Alteration of a single binary bit in the synchronization, frame width, frame rate or time slot and channel allocation can create an entirely new multiplexor that cannot be processed using standard demultiplexor equipment.
Time Multiplexing and Signal Generation
A description for a generic multiplexor is provided below. There are several steps required to digital time multiplex channels of data. All the channels must be digitally formatted. If the channels are analog, i.e., voice, etc., they must be converted through an analog to digital process in order to represent the signal in a digital manner. If the channels are already in digital format then they are ready for multiplexing. Once digital preparation is complete, the channel is then assigned its placement within a framed period of time.
A simple multiplexor frame consists of a binary pattern utilized for time reference sync code at the beginning of the frame followed by a series of timeslots (see FIG. 1). Synchronization may take several frames or several time slots within the frame along a matrix. Timeslots may also be allocated on a multiple frame matrix as well.
The frame is sent at a continuous constant rate, maintaining proper synchronization by the sync code. The timeslots not utilized by the sync code are then available for channel occupation. These timeslots can be allocated to a channel of data individually or in combination to achieve multiple data rates. The number of time slots utilized for each channel is dependent on the needs of the user and the flexibility of the multiplexing equipment.
After the frames have been generated, the data is streamed to a modem for addition of transmission protocols such as forward error correction, randomization and modulation. Common modulations multiplexors use are: on-off keyed, frequency shift keyed, minimum shift keyed, bi-phase shift keyed, quaternary shift keyed, quaternary amplitude modulation and gaussian minimum shift keyed. Basically multiplexors may use any modulation that can be used for binary transmission.
The new signal is sent to a receiving demultiplexor (see FIG. 2) after it is modulated in an analog transmission ready form. The process for demultiplexing and receiving the data in its original format is the reverse of the multiplexing process. The entire multiplexing transformation process is transparent to the users of the multiplexing system.
Prior Art Processing of Time Division Multiplexing (TDM) Signals
Presently, the demultiplexing of TDM signals is based upon single-purpose, fixed solution approaches. Each time a new situation is encountered, it is necessary for the user to manually analyze the signal. After manual analysis the user must then develop an automated or semi-automated system to process that specific TDM signal. This approach has proven to be costly and ineffective as systems are rapidly evolving and being deployed.
Present TDM demultiplexing approaches are hardware intensive and hardware specific. This results in inflexible and expensive systems that are developed to meet a single need specific to the single type of demultiplexing structure. Development dollars become tied up in unwieldy hardware solutions. A simple change in the structure of the multiplexor of interest has the potential to render past solution hardware processing components completely useless.